Zeroth-order polarization propagator approximation

Going one step further and retaining only the zeroth-order contribution to the hessian matrix, i.e. brings us back to the frequency-dependent version of uncoupled Hartree-Fock, Eq. (10.5), sometimes also called the zeroth-order polarization propagator approximation (ZOPPA). 

We have shown that the zeroth-order geometric optics approximation can be used to describe the propagation of normally incident, elliptically polarized light in an inhomogeneous, locally uniaxial medium. The approximation corresponds to finding an asymptotic solution of the wave equation in the short-wavelength limit. It is found that a set of pseudo-Stokes parameters, linearly related to the usual Stokes parameters, can be defined to characterize the propa-... 

A full relativistic theory for coupling tensors within the polarization propagator approach at the RPA level was presented as a generalization of the nonrelativistic theory. Relativistic calculations using the PP formalism have three requirements, namely (i) all operators representing perturbations must be given in relativistic form (ii) the zeroth-order Hamiltonian must be the Dirac-Coulomb-Breit Hamiltonian, /foBC, or some approximation to it and (iii) the electronic states must be relativistic spin-orbitals within the particle-hole or normal ordered representation. Aucar and Oddershede used the particle-hole Dirac-Coulomb-Breit Hamiltonian in the no-pair approach as a starting point, Eq. (18),... 

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